1. Field
The present invention relates generally to wireless communications systems, and more specifically, to systems and methods for optimizing the data transmission capacity of wireless communication systems.
2. Background
The objective of a digital communications receiver is to recover the information sent by the transmitter. In most existing systems, the transmitter introduces a reference signal in the waveform together with the data-bearing signals. This reference signal, commonly referred to as a “pilot signal,” is known a priori by the receiver and is used to increase the efficiency of the demodulation and decoding processes. It is common practice to broadcast the reference signal; in other words, all receivers will be using the same reference signal in their demodulation algorithms.
Since a part of the waveform is devoted to the transmission of the reference signal, the ceiling on system capacity for data transmission decreases as the amount of the reference signal increases. On the other hand, the receiver performance increases with the amount of the reference signal, which directly results in improved data capacity on given channel conditions.
One characteristic of a communication system that utilizes a reference signal is the tradeoff between the data capacity ceiling and the receiver efficiency that results from varying the portion of the waveform devoted to the transmission of the reference signal. Traditionally, the portion of the waveform devoted to the transmission of the reference signal is fixed and is chosen to be a good compromise, or optimization, between improving the receiver's performance and allocating a sufficient portion of the waveform for data transmission. This optimization is performed taking into account all possible channel conditions, which may vary greatly in propagation scenarios like the cellular environment. This leads to a solution which is good for the average case, but which may be far from optimal in extreme channel conditions.
Examples of systems designed to work on the cellular propagation environment are the CDMA standards for voice and data transmissions, cdma2000 and IS-856. It is a common characteristic of these systems to have dedicated traffic channels, i.e., portions of the waveform that are destined only to a particular user, where the information intended for that user is conveyed.
In view of the foregoing, benefits may be realized by systems and methods for improving the overall system capacity for data transmission.